Throughout this application, various publications, patents, and published patent applications are referred to by an identifying citation. The disclosures of the publications, patents, and published patent specifications referenced in this application are hereby incorporated by reference into the present disclosure to more fully describe the state of the art to which this invention pertains.
As the evolution of batteries continues, and particularly as lithium batteries become more widely accepted for a variety of uses, the need for safe, long lasting high energy batteries becomes more important. There has been considerable interest in recent years in developing high energy density cathode-active materials and alkali-metals as anode materials for high energy primary and secondary batteries. Several types of cathode materials for the manufacture of thin film lithium and sodium batteries are known in the art. The most widely investigated group are metallic or inorganic materials which include transition metal chalcogenides, such as titanium disulfide with alkali-metals as the anode as described in U.S. Pat. No. 4,009,052. Also among the cathode active chalcogenides, U.S. Pat. No. 4,049,879 lists transition metal phosphorous chalcogenides, and U.S. Pat. No. 3,992,222 describes cells using mixtures of FeS.sub.2 and various metal sulfides as the electroactive cathode materials. U.S. Pat. No. 3,639,174 describes primary and secondary voltaic cells utilizing lithium aluminum alloy anodes and a reversible cathode depolarizer such as cupric sulfide, cuprous oxide, cupric carbonate, and the like that have low solubility in the electrolyte. U.S. Pat. No. 4,576,697 describes electroactive cathode materials in alkali-metal non-aqueous secondary batteries comprised of carbon-containing intercalatable layered or lamellar transition metal chalcogenides having the general formula M.sub.n X.sub.2 C, wherein M is a transition metal selected from the group consisting of Ti, V, Cr, Fe, Zr, and Ta; X is sulfur; and n is 1-2. High energy density solid state cells comprising cathodes using selected ionically and electronically conductive transition metal chalcogenides in combination with other non-conductive electroactive cathode materials are described in U.S. Pat. No. 4,258,109.
Another type of cathode materials disclosed for use in lithium and sodium batteries are organic materials such as conductive polymers. A further type of organic type cathode materials are those comprised of elemental sulfur, organo-sulfur and carbon-sulfur compositions where high energy density is achieved from the reversible electrochemistry of the sulfur moiety with the alkali metal. U.S. Pat. No. 4,143,214 to Chang et al. describes cells having cathodes containing C.sub.v S wherein v is a numerical value from about 4 to about 50. U.S. Pat. No. 4,152,491 to Chang et al. relates to electric current producing cells where the cathode-active materials include one or more polymer compounds having a plurality of carbon monosulfide units. The carbon monosulfide unit is generally described as (CS).sub.w, wherein w is an integer of at least 5, and may be at least 50, and is preferably at least 100.
U.S. Pat. No. 4,664,991 to Perichaud et al. describes an organo-sulfur material containing a one-dimensional electric conducting polymer and at least one polysulfurated chain forming a charge-transfer complex with the polymer. Perichaud et al. use a material which has two components. One is the conducting or conductive polymer, which is selected from a group consisting of polyacetylenes, polyparaphenylenes, polythiophenes, polypyrroles, polyanilines and their substituted derivatives. The other is a polysulfurated chain which is in a charge transfer relation to the conducting polymer. The polysulfurated chain is formed by high temperature heating of sulfur with the conductive polymer to form appended chains of . . . -S-S-S-S- . . . of indeterminate length.
In a related approach, a PCT application (PCT/FR84/00202) of Armand et al. describes derivatives of polyacetylene-co-polysulfurs comprising units of Z.sub.q (CS.sub.r).sub.n wherein Z is hydrogen, alkali-metal, or transition metal, q has values ranging from 0 to values equal to the valence of the metal ion used, values for r range from greater than 0 to less than or equal to 1, and n is unspecified. These derivatives are made from the reduction of polytetrafluoroethylene or polytrifluorochloroethylene with alkali-metals in the presence of sulfur, or by the sulfuration of polyacetylene with vapors of sulfur monochloride at 220.degree. C.
U.S. Pat. No. 5,441,831 relates to an electric current producing cell which comprises a cathode containing one or more carbon-sulfur compounds of the formula (CS.sub.x).sub.n, in which x takes values from 1.2 to 2.3 and n is equal to or greater than 2.
U.S. Pat. Nos. 4,833,048 and 4,917,974 to De Jonghe et al describe a class of cathode materials made of organo-sulfur compounds of the formula (R(S).sub.y).sub.n where y=1 to 6; n=2 to 20, and R is one or more different aliphatic or aromatic organic moieties having one to twenty carbon atoms. One or more oxygen, sulfur, nitrogen or fluorine atoms associated with the chain can also be included when R is an aliphatic chain. The aliphatic chain may be linear or branched, saturated or unsaturated. The aliphatic chain or the aromatic rings may have substituent groups. The preferred form of the cathode material is a simple dimer or (RS).sub.2. When the organic moiety R is a straight or a branched aliphatic chain, such moieties as alkyl, alkenyl, alkynyl, alkoxyalkyl, alkythioalkyl, or aminoalkyl groups and their fluorine derivatives may be included. When the organic moiety comprises an aromatic group, the group may comprise an aryl, arylalkyl or alkylaryl group, including fluorine substituted derivatives, and the ring may also contain one or more nitrogen, sulfur, or oxygen heteroatoms as well.
In the cell developed by De Jonghe et al. the main cathode reaction during discharge of the battery is the breaking and reforming of disulfide bonds. The breaking of a disulfide bond is associated with the formation of an RS.sup.- M.sup.+ ionic complex. The organo-sulfur materials investigated by De Jonghe et al. undergo polymerization (dimerization) and de-polymerization (disulfide cleavage) upon the formation and breaking of the disulfide bonds. The de-polymerization which occurs during the discharging of the cell results in lower molecular weight polymeric and monomeric species, namely soluble anionic organic sulfides, which can dissolve into the electrolyte and cause self-discharge as well as reduced capacity, thereby severely reducing the utility of the organo-sulfur material as cathode-active material and eventually leading to complete cell failure. The result is an unsatisfactory cycle life having a maximum of about 200 deep discharge-charge cycles, more typically less than 100 cycles as described in J. Electrochem. Soc., Vol. 138, pp. 1891-1895 (1991).
A significant drawback with cells containing cathodes comprising elemental sulfur, organosulfur and carbon-sulfur materials relates to the dissolution and excessive out-diffusion of soluble sulfides, polysulfides, organo-sulfides, carbon-sulfides and/or carbon-polysulfides, hereinafter referred to as anionic reduction products, from the cathode into the rest of the cell. This process leads to several problems: high self-discharge rates, loss of cathode capacity, corrosion of current collectors and electrical leads leading to loss of electrical contact to active cell components, fouling of the anode surface giving rise to malfunction of the anode, and clogging of the pores in the cell membrane separator which leads to loss of ion transport and large increases in internal resistance in the cell.
Composite cathodes containing an electroactive transition metal chalcogenide have been described, typically as a random agglomeration or distribution of the electroactive materials, polymers, conductive fillers, and other solid materials in the cathode layer. In an exception to these homogeneous composite cathodes, U.S. Pat. Nos. 4,576,883, 4,720,910, and 4,808,496 disclose composite cathodes comprising spheres of an electroactive transition metal chalcogenide, such as vanadium pentoxide, encapsulated as a core material in a polymeric shell containing a polymer, an inorganic salt, such as a lithium salt, and optionally, a conductive carbon. These spheres are prepared by an emulsifying or a spray drying process. However, no mention is made in these references of encapsulation by transition metal chalcogenides, of any retarding of the transport of reduced species, of any use with elemental sulfur or sulfur-containing electroactive organic materials, or of any shape of the combined materials other than spheres.
U.S. Pat. No. 3,791,867 to Broadhead et al describes cells containing cathodes consisting of elemental sulfur as the electroactive material present in a layered structure of a transition metal chalcogenide. This patent is directed at preventing the solubilization and transport of the elemental sulfur electroactive material by the electrolyte solvent. It has no mention of the formation of soluble reduced species of the electroactive material, such as soluble sulfides, or of the retarding or control by any means of the transport of these soluble reduced species into the electrolyte layer and other parts of the cell. The transition metal chalcogenides in this patent are limited to sulfides and selenides and do not include transition metal oxides. They are present either as a totally separate layer from the sulfur layer or pressed together with sulfur, in powder form, to provide the composite cathode. There is no mention of any organo-sulfur materials, carbon-sulfur materials, or polymeric binders in the composite cathode. Also there is no mention of improved capacity and battery cycle stability and life by the use of an electroactive transition metal chalcogenide with the elemental sulfur electroactive material.
U.S. Pat. No. 5,324,599 to Oyama et al. discloses composite cathodes containing disulfide organo-sulfur or polyorgano-disulfide materials, as disclosed in U.S. Pat. No. 4,833,048, by a combination with or a chemical derivative with a conductive polymer. The conductive polymers are described as capable of having a porous fibril structure and holding disulfide compounds in their pores. Japanese patent publication number Kokai 08-203530 to Tonomura describes the optional addition of electroactive metal oxide, such as vanadium oxide, to a composite cathode containing disulfide organo-sulfur materials and polyaniline as the conductive polymer. Japanese patent publication number Kokai 08-124570 describes a layered cathode with alternative layers of organo disulfide compound, electroactive metal oxide and conductive polymer with layers of mainly conductive polymers.
In a similar approach to overcome the dissolution problem with polyorganodisulfide materials by a combination or a chemical derivative with a conductive, electroactive material, U.S. Pat. No. 5,516,598 to Visco et al. discloses composite cathodes comprising metal-organosulfur charge transfer materials with one or more metal-sulfur bonds, wherein the oxidation state of the metal is changed in charging and discharging the positive electrode or cathode. The metal ion provides high electrical conductivity to the material, although it significantly lowers the cathode energy density and capacity per unit weight of the polyorgano-disulfide material. This reduced energy density is a disadvantage of derivatives of organo-sulfur materials when utilized to overcome the dissolution problem. The polyorganosulfide material is incorporated in the cathode as a metallic-organosulfur derivative material, similar to the conductive polymer-organosulfur derivative of U.S. Pat. No. 5,324,599, and presumably the residual chemical bonding of the metal to sulfur within the polymeric material prevents the formation of highly soluble sulfide or thiolate anion species. However, there is no mention in these references of retarding of the transport of actual soluble reduced sulfide or thiolate anion species formed during charging or discharging of the cathode. Also, there is no mention in these references of the utility of transition metal chalcogenides, including oxides, in solving the dissolution problem with polyorganodisulfide materials. Instead, the transition metal chalcogenides are mentioned as specifically restricted to their known art of electroactive cathode insertion materials with lithium ions, with no utility with polyorgano-disulfide materials, and with significantly less electrical conductivity than the charge-transfer materials described in these references.
Despite the various approaches proposed for the fabrication of high energy density rechargeable cells containing elemental sulfur, organo-sulfur and carbon-sulfur cathode materials, or derivatives and combinations thereof, there remains a need for materials and cell designs that retard the out-diffusion of anionic reduction products, from the cathode compartments into other components in these cells, improve the utilization of electroactive cathode materials and the cell efficiencies, and provide rechargeable cells with high capacities over many cycles.
It is therefore an object of the present invention to provide composite cathodes containing high loadings of electroactive sulfur-containing cathode material that exhibit a high utilization of the available electrochemical energy and retain this energy capacity without significant loss over many charge-discharge cycles.
It is another object of the present invention to provide composite cathodes, composite cathode materials, and composite cathode designs, for use in rechargeable cells which allow for highly selective transport of alkali-metal ions into and out of the sulfur-containing cathodes while retarding the out-diffusion of anionic reduction products from the cathodes into the cells.
It is a further object of this invention to provide convenient methods for fabricating such composite cathodes.
It is yet a further objective of this invention to provide energy storing rechargeable battery cells which incorporate such composite cathodes, and which exhibit much improved self-discharge characteristics, long shelf life, improved capacity, and high manufacturing reliability.